Various different speech recognition systems are well known and form a large part of our everyday lives. Examples of the well known speech recognition systems include systems for determining airline flight information, systems for accessing billing information, systems for providing directory assistance, systems for allowing service activation, and systems for navigating through a branching tree of possible choices in a customer contact center. Each of these systems processes an utterance by matching it with a single interpretation in the set of all possible interpretations. The set of all possible interpretations of an utterance will be referred to as the “recognition space.” Note that the recognition space in a speech recognition system is always finite.
All speech recognition systems require an accurate interpretation of an utterance to perform an appropriate action; however, speech recognition systems are not foolproof and use probabilities to determine the likeliness of each possible utterance interpretation. A number of factors affect speech recognition accuracy, including the phonetic distinctiveness of items in the recognition space, the ability of system users to dynamically change the recognition space, the accent of a person issuing an utterance, simple mispronunciations, and so on. Each of these factors is greatly affected by the size of the recognition space. A large recognition space increases the likelihood of confusability and causes all of the factors that impact speech recognition to become severe problems.
One example of a potentially very large recognition space is a directory of user names, which can exist when a communications system has a large number of users who rely on voice commands to contact each other. This problem grows as the communications system itself grows, effectively providing a limit to the continued success of the system. All communications systems, such as telephones or fax machines, become more useful as more people employ them. When a communications system with a spoken user directory acquires a large number of users, however, the size of the directory itself limits the effectiveness of the system, because it significantly reduces the accuracy of speech recognition.
A speech recognition system would realize a significant benefit by being able to find accurate interpretations of similarly spelled or sounding names in a large recognition space, especially when one or more of the following situations occur: entries in the recognition space change dynamically and/or the recognition space contains entries that are not phonetically distinctive.